Thiopental Sodium

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Thiopental Sodium contains NLT 97.0% and NMT 102.0% of thiopental sodium (C₁₁H₁₇N₂NaO₂S), calculated on the dried basis.

2 IDENTIFICATION

A.

Sample: 500 mg of Thiopental Sodium

Analysis: Dissolve the Sample in 10 mL of water in a separator, add 10 mL of 3 N hydrochloric acid, and extract the liberated thiopental with two 25-mL portions of chloroform. Evaporate the combined chloroform extracts to dryness. Add 10 mL of ether, evaporate again, and dry at 105° for 2 h.

Acceptance criteria: The IR absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Thiopental RS.

B. Identification Tests—General, Sodium〈191〉

Analysis: Ignite 500 mg.

Acceptance criteria: The residue meets the requirements.

C.

Sample: 200 mg of Thiopental Sodium

Analysis 1: Dissolve the Sample in 5 mL of 1 N sodium hydroxide, and add 2 mL of lead acetate TS.

Acceptance criteria 1: A white precipitate is formed, and it gradually darkens when the mixture is boiled.

Analysis 2: Acidify the darkened mixture obtained from Analysis 1 with hydrochloric acid.

Acceptance criteria 2: Hydrogen sulfide is evolved, and it is recognizable by its darkening of moistened lead acetate test paper held in the vapor.

3 ASSAY

Procedure

Solution A: 4 g/L of sodium hydroxide

Standard solution: 5 μg/mL of USP Thiopental RS in Solution A

Sample solution: 5 μg/mL of Thiopental Sodium in Solution A

Instrumental conditions

Mode: UV

Analytical wavelength: 304 nm

Cell: 1 cm

Blank: Solution A

Analysis

Samples: Standard solution, Sample solution, and Blank

Calculate the percentage of thiopental sodium in the portion of Thiopental Sodium taken:

Result = (A_U/A_S) × (C_S/C_U) × (M_r1/M_r2) × 100

A_U = absorbance of the Sample solution

A_S = absorbance of the Standard solution

C_S = concentration of USP Thiopental RS in the Standard solution (μg/mL)

C_U = concentration of Thiopental Sodium in the Sample solution (μg/mL)

M_r1 = molecular weight of thiopental sodium, 264.32

M_r2 = molecular weight of thiopental, 242.34

Acceptance criteria: 97.0%–102.0% on the dried basis

4 IMPURITIES

Ordinary Impurities 〈466〉

Standard solution: 9.2 mg/mL of USP Thiopental RS in methanol

Sample solution: 10 mg/mL of Thiopental Sodium in methanol

Application volume: 40 μL

Eluant: Toluene and methanol (85:15)

Visualization: 1

Acceptance criteria: Meets the requirements

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry at 80° for 4 h.

Acceptance criteria: NMT 2.0%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

USP Reference Standards 〈11〉

USP Thiopental RS